This invention relates to a method of controlling the fuel supply to internal combustion engines at acceleration, and more particularly to a method of this kind which increases the quantity of fuel to be injected into the engine at acceleration by an accelerating fuel increment which is set to a value optimal for the accelerating condition of the engine.
A fuel supply control method for internal combustion engines is known e.g. from Japanese Provisional Publication (Kokai) No. 60-3458, which is capable of preventing so-called accelerating shock at acceleration of the engine and also improving accelerability of the engine. According to this fuel supply control system, one table group is selected from predetermined table groups for determining the value of an accelerating fuel increment TACC in dependence on an operating condition in which the engine is operating, i.e. whether the engine is in a high speed operating region, whether the engine is in an accelerating condition immediately after termination of a fuel cut operation, whether the engine coolant temperature is in a low temperature region, etc. Then, a different table is selected from the aforementioned selected table groups in accordance with each pulsed of a control signal generated at each of predetermined crank angle positions of the engine after first detection of the accelerating condition of the engine, e.g. a signal indicative of the top dead center (TDC). Finally, a value of the accelerating fuel increment TACC is read out from the selected table in response to the opening speed of the throttle valve. Each table is set such that a value of the accelerating fuel increment initially read out is a large value for initial acceleration of the engine, and thereafter gradually decreased values are read out as further pulses of TDC signal are generated.
According to the above described conventional method, the accelerating increment TACC value in each selected table is always read out only in response to the opening speed .DELTA..theta. of the throttle valve. In addition, the accelerating increment TACC is generally set at values as to be assumed when the throttle valve is opened to fully open position or the maximum opening degree. However, even though the opening speed of the throttle valve shows the same value, there can be various modes of opening the throttle valve according to respective different ways of driving the engine, e.g. a mode of opening the throttle valve from an almost fully closed position to a medium opening position, and a mode of opening the valve from an almost fully closed position to a fully opened position. Particularly, when the opening speed of the throttle valve shows a large value at the initial stage of acceleration and the throttle valve is opened only to a small or medium opening position, the accelerating increment TACC will be set to the same value as that for a high load condition of the engine although the engine is actually operating in a low or middle load condition. As a result, the mixture to be supplied to the engine becomes overrich, which can badly affect the emission characteristics of the engine and can often cause so-called after-fire.